We report the first result from a dark photon dark matter search in the mass
range from
78.62 to
83.95 μeV/c2 with a dielectric haloscope
prototype for MADMAX (Magnetized Disc and Mirror Axion eXperiment). Putative
dark photons would convert to observable photons within a stack consisting of
three sapphire disks and a mirror. The emitted power of this system is received
by an antenna and successively digitized using a low-noise receiver. No dark
photon signal has been observed. Assuming unpolarized dark photon dark matter
with a local density of
ρχ=0.3 GeV/cm3 we exclude a dark
photon to photon mixing parameter
χ>2.7×10−12 over the full
mass range and
χ>1.1×10−13 at a mass of $80.57~\mathrm{\mu
eV}/c^2$ with a 95\% confidence level. This is the first physics result from a
MADMAX prototype and exceeds previous constraints on
χ in this mass range
by up to almost three orders of magnitude.